Field of the Invention
The invention relates to a semiconductor chip having at least one capacitor and an electrically insulating layer that forms a dielectric for the capacitor, as well as an evaluation circuit which disables the semiconductor chip if the layer is removed.
Such a semiconductor chip is known from U.S. Pat. No. 4,868,489. In that patent, the dielectric property of the passivation layer of the semiconductor chip is used in order to make it possible to detect a removal of this passivation layer. However, this detection is carried out only by a direct measurement of the capacitance of two neighboring metallic surfaces.
Published German Patent Application DE 40 18 688 A1 discloses detecting the capacitance, inductance and resistance of a conducting surface, which is applied to the semiconductor chip surface and covers the underlying circuits, in order to make it possible to ascertain when this protective layer has been removed. This involves however determining the capacitance relative to the underlying layers. Furthermore, the inductance of such a surface is very small, so that an evaluation requires circuits which are highly sensitive and therefore elaborate and expensive.
The costs involved in developing an integrated circuit, hereinafter referred to as semiconductor chip, are known to be very high, while production costs, in particular in very large production runs, may be comparatively low. Semiconductor chips are therefore exposed to the risk of being analyzed and copied without permission. For this reason, as already indicated above, various measures have been developed which are intended to prevent unauthorized analyzing of the way in which a semiconductor chip functions, as well as its structure.